Carburetor fuel bowl vent

ABSTRACT

A light metal fuel bowl vent valve disc is pressure responsive to allow automatic venting of the bowl. A resilient arm is attached at one end to the fuel bowl cover and is curled at the other end to engage and open the valve disc. The arm is moved by a radially extending flange attached to the top of an accelerator pump stem or spring retainer. The arm is adjustable relative to the flange to open the valve only when the pump is near its uppermost position. In one embodiment the arm carries and is moved by an adjustment screw which engages the flange, whereas in a second embodiment the arm has lower and upper portions which are spread by an adjustment screw and a tang extending from the upper portion of the arm engages the flange.

United States Patent [1 1 Taylor [4 1 Sept. 9, 1975 CARBURETOR FUEL BOWLVENT Roland S. Taylor, Fairport, NY.

General Motors Corporation, Detroit, Mich.

[22] Filed: Jan. 25, 1974 [21] Appl. No.: 436,492

[75] Inventor:

[73] Assignee:

[52] U.S. Cl 261/34 A; 261/72 R; 261/DIG. 67

[51] Int. Cl. F02m 5/08 [58] Field of Search 261/34 A, 72 R, DIG. 67

[56] References Cited UNITED STATES PATENTS 2,741,465 4/1956 Redman eta1 26l/DIG. 67 2,867,423 1/1959 Wing 261/DIG. 67 3,001,774 9/1961 Sartot .1 261/42 3,110,749 11/1963 Marsee 261/34 A Primary Examiner Tim R.Miles Attorney, Agent, or FirmC. K. Veenstra 57 ABSTRACT A light metalfuel bowl vent valve disc is pressure responsive to allow automaticventing of the bowl. A re silient arm is attached at one end to the fuelbowl cover and is curled at the other end to engage and open the valvedisc. The arm is moved by a radially I extending flange attached to thetop of an accelerator pump stem or spring retainer. The arm isadjustable relative to the flange to open the valve only when the pumpis near its uppermost position. In one embodiment the arm carries and ismoved by an adjustment screw which engages the flange, whereas in asecond embodiment the arm has lower and upper portions which are spreadby an adjustment screw and a tang extending from the upper portion ofthe arm engages the flange.

3 Claims, 4 Drawing Figures PATENTED SEP 91975 saw 2 0f 2 CARBURETORFUEL BOWL VENT This invention relates to carburetors for internalcombustion engines and, more paticularly, to carburetors having meanswhich vent the carburetor fuel bowl when the accelerator pump is nearits uppermost position.

In the operation of carburetors, it is desirable to vent the fuel bowlif an excess amount of fuel vapor is produced by the fuel therein, aswhen the engine is hot and the throttle is closed. This might occurduring idling, deceleration, or immediately after the engine is stopped,i.e. a hot soak. The accumulation of vapor in the top of the fuel bowlcan be minimized by venting the top of the fuel bowl to the atmosphereor to a vapor collection canister for subsequent return to thecarburetor.

Means for venting carburetor fuel bowls during closed throttle operationhave been provided in the past. For example, in U.S. Pat. No. 2,867,423Wing a carburetor bowl vent valve is described which is operated by thethrottle and opens when the throttle valve is closed. Also, springbiased rubber vent valves coacting with the accelerator pump linkagehave been used for closed throttle venting, as have light metal valvediscs for automatic, self-venting. Some vent valves have been opened bylinkage extending from the carburetor accelerator pump, which is adesirable feature since the accelerator pump is normally in an uppermostposition during closed throttle operation of the engine.

It is the principal object of the present invention to provide means foroperating a carburetor fuel bowl vent valve comprising a resilientactuating arm engaged by a radially extending flange attached to theaccelerator pump stem, and effective to open the valve only when theaccelerator pump is near its uppermost position which occurs when thethrottle is closed. In a preferred embodiment, the environmentsurrounding the present invention includes a fuel vapor region in thetop of the carburetor fuel bowl has a passage extending from an aperturein the top of this bowl to a vapor collection canister to obtain a vaporventing system which minimizes vapor loss to the atmosphere. The valveis essentially a round plate of light metal which sealingly seats in theaperture to prevent vapor discharge from the bowl when the bowl vaporpressure is insufficient to unseat the disc, but will allow the bowl tovent if such pressure is excessive.

There are two illustrated embodiments of the operating arm but both haveseveral features in common: one end of the arm is secured to the top ofthe carburetor, the other end is a finger portion which moves the valve,and both have adjustment screws which vary the opening time of thevalve. The difference between the embodiments lies in the manner inwhich the arms are adjusted relative to and engage the accelerator pumpflange, and this distinction will be made more apparent as thedescription proceeds.

Other objects and features of the invention will become apparent as thedescription proceeds in the specification, especially when taken inconjunction with the accompanying drawings, illustrating preferredembodiments of the invention, wherein:

FIG. 1 is an elevational view of a carburetor with parts broken away toillustrate the air inlet for air flow to the engine, the acceleratorpump, and the pump discharge passage;

FIG. 2 is an enlarged sectional view taken along line 22 of FIG. 1,showing the fuel bowl vent valve and one embodiment of the adjustablevent valve operating arm; 1

FIG. 3 is a view similar to FIG. 2 and illustrates a second embodimentof the adjustable vent valve operating arm; and

FIG. 4 is an enlarged view taken along line 4-4 of FIG. 3 and showingthe details of the adjustable vent valve operating arm.

Referring first to FIG. 1, the carburetor 10 has a mixture conduit 12including an air inlet 14 and a mixture outlet 16 which discharges tothe engine. A throttle 18 is disposed in mixture outlet 16 in the usualmanner on the throttle shaft 20.

Mixture conduit 12 has a venturi-type restriction 22 formed betweeninlet 14 and outlet 16 of the mixture conduit 12, but it should be notedthat the present invention need not be restricted to carburetors of theventuri type. For example, it could be used as well in an air valvecarburetor having a covered fuel bowl, an accelerator pump, and linkagebetween the throttle and pump.

Continuing with the description of FIG. 1, a throttle lever 24 issecured to throttle shaft 20. A link 26 is pivotally connected at oneend 28 to throttle lever 24. The other end 30 of link 26 is pivotallyconnected to one end 32 of an accelerator pump lever 34. Pump lever 34is pivoted on carburetor 10 by means of a pivot pin 36. The opposite end38 of pump lever 34 abuts an end 40 of a pump stem 42, thus operativelyconnecting throttle lever 24, link 26, pump lever 34 and pump stem 42.

An accelerator pump assembly 44 comprises pump stem 42 centrally andreciprocably disposed through a guide portion 46 formed in the fuel bowlcover 47 of carburetor l0. Slidably disposed on the lower end 48 of stem42 is a pump plunger 50. Plunger 50 is disposed in a vertical pump bore52 formed in carburetor l0 and has a cup seal member 54 abutting butslidingly disposed in pump bore 52. Cup seal 54 acts as a fuel checkvalve in a manner to be described.

Plunger 50 is urged toward its uppermost position by means of a returnspring 56, one end of which resides in the bottom of bore 52 and theother end of which abuts the lower side of plunger 50, thereby urgingplunger 50 upwardly.

The rate of discharge of fuel from a discharge portion 58 of bore 52formed between plunger 50 and the bottom of the bore 52 is controlled inpart by a stiff duration spring 60. The lower end '61 of duration spring60 resides on a flange 62 radially extending from plunger 50. The upperend of duration spring 60 is restrained and compressed by means of aspring retainer 64 residing under a flange 82 on a shoulder portion 63of pump stem 42.

In operation, when plunger 50 moves upward in pump bore 52, fuel flowsfrom the fuel bowl 65 through a slot 66 in the top of the pump bore 52and is passed by the skirt of the cup seal 54 into the discharge portion58. It should be noted that in a preferred embodiment cup seal 54 is aso-called floating type, whereby cup seal 54 slides up and down on atapered portion 67 of plunger 50. When the plunger 50 is moved upward,the flat 68 on the top of the cup seal 54 unseats from the associatedflat on the plunger 50. This vents vapors which otherwise may be trappedin discharge portion 58 so that a solid charge of fuel can be maintainedbeneath plunger 50 for subsequent pump strokes. when plunger 50 islowered, flat 68 on cup seal 54 seals against the associated flat on theplunger and the skirt on cup seal 54 is biased outwardly against thewall of bore 52 to prevent fuel flow therearound. In this manner, cupseal 54 acts as a fuel check valve for filling discharge portion 58.

A pump discharge passage 70 connects discharge portion 58 through a pumpjet 72 to mixture conduit 12. During high speed operation, a vacuumexists on the downstream side of pump jet 72. Therefore, a cavity 74upstream of pump jet 72 is provided which vents discharge passage 70 tothe atmosphere outside the air inlet 14. Cavity 74 acts as a suctionbreaker so that when the pump 44 is not in operation, fuel will not bepulled out of pump jet 72 into the venturi area 22. This suction breakerensures a full pump discharge when needed and prevents any siphoning orfuel pullover from pump 44 and discharge passage 70.

A discharge check ball 76 is disposed in discharge passage 70 and isvertically constrained by a ball retainer 77 which allows ball 76 torise a selected height above a seat 79 formed in passage 70. Duringupward motion of plunger 50, check ball 76 is drawn against and therebyscals seat 79 so that air will not be drawn into discharge portion 58.

When throttle valve 18 is opened, the connecting linkage comprisinglever 24, link 26 and lever 34 forces stem 42 and duration spring 60downward. Stem 42 may move relative to plunger 50 by means of a recess80 in the plunger. Spring 60 in turn forces plunger 50 downward at arate determined, in part, by the stiffness of spring 60 and the size ofpassage 70. As soon as plunger 50 moves, it displaces fuel upwardlywhich seats pump cup 54 on radially extending flange 62 of plunger 50.The further downward movement of plunger 50 forces fuel from dischargeportion 58 of bore 52 through the fuel discharge passage 70. Thereupon,fuel flow unseats check ball 76 and passes on through passage 70 to pumpjet 72 for delivery to mixture conduit 12.

When the throttle is closed this repositions lever 24, link 26 and lever34 to the position shown in FIG. 1.

Accordingly, spring 56 is effective to move plunger 50 upwardly and inturn this moves the lower end of spring 60 upwardly. This moves springretainer 64 upwardly until spring 56 has fully expanded and stem 42 andretainer 64 are an aan uppermost position as shown in FIG. 1.

Referring to FIG. 2, the present invention will now be described indetail. A radially extending actuating plate or flange 82 is attached toor extends from spring retainer 64. Alternatively, flange 82 may residebetween a shoulder portion 63 of stem 42 and retainer 64. A resilientvalve operating arm 86 is secured at one end 87 to the underside of thecover 47 of fuel bowl 65. Operating arm 86 threadedly carries anadjusting screw 88 which engages flange 82 and lifts arm 86 as stem 42nears its uppermost position during throttle closing movement. It shouldbe noted that the resiliency or downward bias of arm 86 offersnegligible resistance to the upward movement of stem 42.

The other end of arm 86 is a curled finger 89 which smoothly engages avalve disc 90 seated on a valve seat 92 formed in or staked to the cover47 of the fuel bowl 65. This coaction between disc 90 and seat 92 sealsan aperture 93 opening from a fuel vapor region 94 formed below cover 47within bowl 65, When the throttle is closed and stem 42 is raised byspring 56, adjusting screw 88 carried on arm 86 is engaged by flange 82and arm 86 moves upwardly. Thereupon, finger 89 slides under andsmoothly lifts disc from seat 92. This permits fuel vapor to flow out ofthe fuel vapor region 94 through an opening 95 and a cavity 96 formed incover 47 to a hose fitting 98 which is connected, for example, to a fuelvapor storage canister 99. The sliding action between finger 89 and disc90 ensures that the venting process will proceed smoothly andunrestricted.

As the pump stem 42 moves downwardly during throttle opening movement,arm 86 moves downwardly under an inherent spring force to a lowerposition. As arm 86 moves downward, finger 89 disengages disc 90. Thispermits disc 90 to seat on valve seat 92 to prevent vapor flow fromregion 94 through aperture 93, opening 95 and cavity 96 to vapor storagecanister 99.

However, valve disc 90 is, in the preferred embodiment, fashioned fromlight metal so as to be also responsive to bowl vapor pressure. Shouldthe vapor pressure in vapor region 94 become adequate to overcome theweight of disc 90, the valve is forced upwardly to open aperture 93.Accordingly, excess vapor pressure is allowed to vent from region 94through aperture 93, opening 95 and cavity 96 to vapor storage canister99. This continues until the vapor pressure below valve 90 is reduced toa point where it is insufficient to raise the disc, thereby allowing thevalve to close.

It should also be noted that disc 90 is free to rotate or float in achamber 100 above aperture 93, so that the propensity for valve 90 tostick to seat 92 is minimized. A boss 101 extending downwardly inchamber 100 limits the vertical travel of the disc.

It should be noted that as screw 88 is turned it moves and thus variesthe interengagement position between screw 88 and flange 82. This inturn varies the time in the accelerator pump return stroke at whichflange 82 engages screw 88 and disc 90 is lifted. For example, if screw88 is turned downwardly it will engage flange 82 at a lower point in thepump upward travel than would occur if screw 88 had been moved upwardly.Accordingly, arm 86 and finger 89 will move earlier during the pumpreturn stroke or, more significantly, farther from closed throttle. andopen the valve before the pump reaches its uppermost position.

It can therefore be seen that a continuum of interengagement pointsbetween screw 88 and flange 82 is available and is limited only by thelength and position of screw 88 thereby providing a range of openingtimes of valve disc 90 relative to throttle position, which permitsventing at a certain throttle position, at or near closed throttle.Accordingly, fuel vapor, which the engine may not be capable ofcompletely burning if it were discharged through internal vent passagesmay be vented away from the carburetor.

An alternative embodiment of the present invention is shown in FIG. 3,in which a modified form of the valve actuating spring 86 is designated86'. It should be recognized that the environment of the arm isidentical to that heretofore described, and modified componentscomprising the present invention are designated with primed referencenumerals in the FIG. 3 embodiment.

Proceeding with the details of FIG. 3, spring arm 86' is secured at oneend 87 to the cover 47' of the fuel finger portionfli89' which isdisposed off-center of the .valve .disc 90. It should be appreciatedthatthe curled finger 89' is provided to open valve disc 90 in the manner,illustrated by the phantom position of arm-8 6'. The curledfinger,89f.-slides smoothly under valve disc 90. This sliding actionensures that the venting process will proceed-smoothly and unrestricted.Abos s101 extending downwardly into chamber 100 above-disc 90 limits thetravel of disc.;9 0 in a manner identical to theFlG. 2 embodiment. 1

Spring arm 86 extends back upon itself about curled finger 89" in 'aconforming manner and forms an inter mediate humpedportion; 102 whichextends downwardly to a tang 104. Tang 104 extends through an aperture1-06 formed'in thelower portion 108 of arm 86 and may abut and engageradially extending flange 82 ridingon spr'ing retainer. 64, When'flange82 engages tang 104, this moves arm 86' aiid raises finger portion 89'to engage: valve disc 90. Accordingly, vapors in region 94 mayflowthrough apertufe 93,,opening 95 and cavity 96 to vapor storage'canis'ter 9 9. l M

An adjustment screw 88" is threadedly carried by humped portion 102 andabuts the lowe r portion 108 of spring arm 86". Asl'adjustment screw 88"is turned, it lifts the humped portion 102 from the lowerportion s ofarm 86. Accordingly, tang 104 is raised relative to curled fingerportion 89. This adjusts the position of finger 89 relative to flange 82to control the time of opening of valve 90 in a manner analogous to theFIG. 2 embodiment.

Referring to FIG. 4, further details of the spring arm 86 can beobserved. Fixed end 87 of the arm is secured to the cover 47 of fuelbowl 65 by means of two screws 110. Aperture 106, formed in the lowerportion 108 of the spring arm 86, allows movement of the arm about pumpstem 42. Downwardly extending tang 104 protrudes through aperture 106 toengage the radially extending flange 82 carried by retainer 64.Adjustment screw 88' is shown in phantom above the lower portion 108 ofarm 86. Lower portion 108 extends to the curled finger 89 and turns backupon itself so that it resides under the upper or humped portion 102 ofthe arm.

Adjustment of the operating arm in either embodiment is facilitated byan opening 111 formed in cover 47 through which a driver may be insertedto turn screw 88 (88) after the carburetor is assembled. A cover plateor plug 112 may be used to sealingly close opening 111 after adjustmentis completed to prevent loss of fuel vapor therethrough.

Thus, it will be seen that in accordance with the invention, acarburetor fuel bowl vent valve 90 is operated when the accelerator pump44 is in its uppermost position by means of an adjustable, resilientoperating arm 86 (86'). It should be noted that adjustment screw 88(88') is threadedly carried by the arm to adjust the position of the armrelative to the pump stern flange to ensure venting of the carburetorfuel bowl whenever the pump is in its uppermost position. i A

Although the preferred embodiments and method of operation of thepresent invention have been described, the present invention is not tobe limited by the foregoing description, but as set forth in thehereinafter appended claims.

What is claimed is:

1. An internal combustion engine carburetor having an air inlet for airflow to the engine, a throttle disposed in said air inlet and movablebetween closed and open positions for. controlling air flowtherethrough, a fuel bowl, said fuel bowl having a fuel vapor region inits upperportion, a cover member for said fuel bowl said cover memberhaving a vent aperture opening from said region for discharging fuelvapor therefrom and a valve seat surrounding said aperture, a vent valvebiased into engagement with said valve seat for controlling the flow offuel vapor throughsaid aperture, an accelerator pump bore verticallydisposed in said carburetor, an accelerator pump plunger disposed insaid bore and defining a discharge chamber within said bore, inlet meansfor supply fuel from said fuel bowl to said chamber, a discharge passagefor delivering fuel from saidchamber'to said air inlet, a stem forreciprocating said plunger within said bore to discharge fuel from saidchamber through said passage to said inlet when said stern movesdownwardly, said stem having a radially extending flange, and. linkgagemeans operatively connecting said stem with said throttle for movingsaid stem upwardly as said throttle is moved to said closed position anddownwardly as said throttle is moved to said open position, wherein theimprovement comprises: a resilient valve operating arm movable between alower and a'raised position, said arm having one end secured to saidcover member, said arm having another end engageable with said ventvalve when said arm is in said raised position, said arm including meanswhich engages said flange only when said pump is near its uppermostposition to lift said arm to said raised position whereby said other endof said arm engages and lifts said valve from said valve seat, said armbeing biased from said raised position whereby said arm returns to saidlower position and disengages said valve when said pump is below saidposition.

2. An internal combustion engine carburetor having an air inlet for airflow to the engine, a throttle disposed in said air inlet and movablebetween closed and open positions for controlling air flow therethrough,a fuel bowl, said fuel bowl having a fuel vapor region in its upperportion, a cover member for said fuel bowl having a vent apertureopening from said region for discharging fuel vapor therefrom and avalve seat surrounding said aperture, a vent valve biased intoengagement with said valve seat for controlling the flow of fuel vaporthrough said aperture, an accelerator pump bore vertically disposed insaid carburetor, an accelerator pump plunger disposed in said bore anddefining a discharge chamber within said bore, inlet means for supplyingfuel from said fuel bowl to said chamber, a discharge passage fordelivering fuel from said chamber to said air inlet, a stem forreciprocating said plunger within said bore to discharge fuel from saidchamber through said passage to said inlet when said stem movesdownwardly, said stem having a radially extending flange, and linkagemeans operatively connecting said stem with said throttle for movingsaid stem upwardly as said throttle is moved to said closed position anddownwardly as said throttle is moved to said open position, wherein theimprovement comprises: a resilient valve operating arm having one enddisposed adjacent said valve and having the other end secured to theunderside of said cover member, said arm being movable between a loweredand a raised position, and an adjustment screw theadedly carried by saidarm and engaging said flange of said stern as said throttle is movedtoward said closed position whereby said arm is raised from said loweredposition to engage and lift said valve from said valve seat, said screwdisengaging said flange as said throttle is moved from said closedposition whereby said arm is lowered from said raised position and isdisengaged from said valve.

3. An internal combustion engine carburetor having an air inlet for airflow to the engine, a throttle disposed in said air inlet and movablebetween closed and open positions for controlling air flow therethrough,a fuel bowl, said fuel bowl having a fuel vapor region in its upperportion, a cover member for said fuel bowl having a vent apertureopening from said region for discharging fuel vapor therefrom, and avalve seat surrounding said aperture, a vent valve biased intoengagement with said valve seat for controlling the flow of fuel vaporthrough said aperture, an accelerator pump bore vertically disposed insaid carburetor, an accelerator pump plunger disposed in said bore anddefining a discharge chamber within said bore, inlet means for supplyingfuel from said fuel bowl to said chamber, a discharge passage fordelivering fuel from said chamber to said air inlet, a stem forreciprocating said plunger within said bore to discharge fuel from saidchamber through said passage to said inlet when said stem movesdownwardly, said stem having a radially extending flange, and linkagemeans operatively connecting said stem with said throttle for movingsaid stem upwardly as said throttle is moved to said closed position anddownwardly as said throttle is moved to said open position wherein theimprovement comprises: a resilient valve operating arm having one endsecured to the underside of said cover member and the other end forminga finger portion, said arm having a lower portion with an apertureformed therein, said stem protruding through said aperture, said armfurther having an upper humped portion carrying a tang extendingdownwardly through said aperture to engage said flange, said upperhumped portion disposed above said lower portion between said securedend and said finger portion, said arm being movable between a loweredand a raised position, and an adjusting screw threadedly carried by saidupper humped portion and abutting said lower portion, whereby saidadjusting screw moves said hump portion relative to said lower portionto reposition said tang thereby varying the time at which said tangengages said flange as said throttle is moved toward said closedposition, and whereby as said throttle is moved toward said closedposition said tang is moved by said flange and raises said arm to saidraised position so that said finger portion opens said valve, and assaid throttle is moved away from said closed position said tangdisengages said flange and said arm is lowered from said raised positionand is disengaged from said valve.

l l l

1. A INTERNAL COMBUSTION ENGINE CARBURETOR HAVING AN AIR INLET FOR AIRFLOW TO THE ENGINE, A THROTTLE DISPOSED IN SAID AIR INLET AN MOVABLEBETWEEN CLOSED ANDOPEN POSITIONS FOR CONTROLLING AIR FLOW THERETHROUGH,A FUEL BOWL, SAID FUEL BOWL HAVING A FUEL VAPOR REGION IN ITS UPPERPORTION, A COVER MEMBER FOR SAID FUEL BOWL, SAID COVER MEMBER HAVINGAVENT APERTURE OPENING FROM SAID REGION FOR DISCHARGING FUEL VAPORTHEREFROM AND A VALVE SEAT SURROUNDING SAID APERTURE, A VENT VALVEBIASED INTO ENGAHEMENT WITH SAID VALVE SEAT FOR CONTROLLING THE FLOW OFFUEL VAPOR THROUGH SAID APERTURE, AN ACCELERATOR PUMP BORE VERTICALLYDISPOSED IN SAID CARBURETOR, AN ACCELERATOR PUMP PLUNGER DISPOSED INSAID BORE AND DEFINING A DISCHARGE CHAMBER WITHIN SAID BORE, INLET MEANSFOR SUPPLY FUEL FROM SAID FUEL BOWL TO SAID CHAMBER, A DISCHARGE PASSAGEFOR DELIVERING FUEL FROM SAID CHAMBER TO SAID AIR INLET, A STEM FORRECIPROCATING SAID PLUNGER WITHIN SAID BORE TO DISCHARGE FUEL FROM SAIDCHAMBER THROUGH SAID PASSAGE TO SAID INLET WHN SAID STEM MOVESDOWNWARDLY, SAID STEM HAVING A RADIALLY EXTENDING FLANGE, AND LINKGAGEMEANS OPERATIVELY CONNECTING SAID STEM WITH SAID THROTTLE FOR MOVINGSAID STEM UPWARDLY AS SAID THROTTLE IS MOVED TO SAID CLOSED POSITION ANDDOWNWARDLY AS SAID THROTTLE IS MOVED TO SAID OPEN POSITION, WHEREIN THEIMPROVEMENT COMPRISES: A RESILIENT VALVE OPERATING ARM MOVABLE BETWEEN ALOWER AND A RAISED POSITION, SAID ARM HAVING ONE END SECURED TO SAIDCOVER MEMBER, SAID ARM HAVING ANOTHER END ENGAGEABLE WITH SAID VENTVALVE WHEN SAID ARM IS IN SAID RAISED POSITION, SAID ARM INCLUDING MEANSWHICH ENGAGES SAID FLANGE ONLY WHEN SAID PUMP IS NEAR ITS UPPERMOSTPOSITION TO LIFT SAID ARM TO SAID RAISED POSITION WHEREBY SAID OTHER ENDOF SAID ARM ENGAGES AND LIFTS SAID VALVE FROM SAI VALVE SEAT, SAID ARMBEING BIASED FROM SAID RAISED POSITION WHEREBY SAID ARM RETURNS TO SAIDLOWER POSITION AND DISENGAGES SAID VALVE WHEN SAID PUMP IS BELOW SAIDPOSITION.
 2. An internal combustion engine carburetor having an airinlet for air flow to the engine, a throttle disposed in said air inletand movable between closed and open positions for controlling air flowtherethrough, a fuel bowl, said fuel bowl having a fuel vapor region inits upper portion, a cover member for said fuel bowl having a ventaperture opening from said region for discharging fuel vapor therefromand a valve seat surrounding said aperture, a vent valve biased intoengagement with said valve seat for controlling the flow of fuel vaporthrough said aperture, an accelerator pump bore vertically disposed insaid carburetor, an accelerator pump plunger disposed in said bore anddefining a discharge chamber within said bore, inlet means for supplyingfuel from said fuel bowl to said chamber, a discharge passage fordelivering fuel from said chamber to said air inlet, a stem forreciprocating said plunger within said bore to discharge fuel from saidchamber through said passage to said inlet when said stem movesdownwardly, said stem having a radially extending flange, and linkagemeans operatively connecting said stem with said throttle for movingsaid stem upwardly as said throttle is moved to said closed position anddownwardly as said throttle is moved to said open position, wherein theimprovement comprises: a resilient valve operating arm having one enddisposed adjacent said valve and having the other end secured to theunderside of said cover member, said arm being movable between a loweredand a raised position, and an adjustment screw theadedly carried by saidarm and engaging said flange of said stem as said throttle is movedtoward said closed position whereby said arm is raised from said loweredposition to engage and lift said valve from said valve seat, said screwdisengaging said flange as said throttle is moved from said closedposition whereby said arm is lowered from said raised position and isdisengaged from said valve.
 3. An internal combustion engine carburetorhaving an air inlet for air flow to the engine, a throttle disposed insaid air inlet and movable between closed and open positions forcontrolling air flow therethrough, a fuel bowl, said fuel bowl having afuel vapor region in its upper portion, a cover member for said fuelbowl having a vent aperture opening from said region for dischargingfuel vapor therefrom, and a valve seat surrounding said aperture, a ventvalve biased into engagement with said valve seat for controlling theflow of fuel vapor through said aperture, an accelerator pump borevertically disposed in said carburetor, an accelerator pump plungerdisposed in said bore and defining a discharge chamber within said bore,inlet means for supplying fuel from said fuel bowl to said chamber, adischarge passage for delivering fuel from said chamber to said airinlet, a stem for reciprocating said plunger within said bore todischarge fuel from said chamber through said passage to said inlet whensaid stem moves downwardly, said stem having a radially extendingflange, and linkage means operatively connecting said stem with saidthrottle for moving said stem upwardly as said throttle is moved to saidclosed position and downwardly as said throttle is moved to said openposition wherein the improvement comprises: a resilient valve operatingarm having one end secured to the underside of said cover member and theother end forming a finger portion, said arm having a lower portion withan aperture formed therein, said stem protruding through said aperture,said arm further having an upper humped portion carrying a tangextending downwardly through said aperture to engage said flange, saidupper humped portion disposed above said lower portion between saidsecured end and said finger portion, said arm being movable between alowered and a raised position, and an adjusting screw threadedly carriedby said upper humped portion and abutting said lower portion, wherebysaid adjusting screw moves said hump portion relative to said lowerportion to reposition said tang thereby varying the time at which saidtang engages said flange as said throttle is moved toward said closedposition, and whereby as said throttle is moved toward said closedposition said tang is moved by said flange and raises said arm to saidraised position so that said finger portion opens said valve, and assaid throttle is moved away from said closed position said tangdisengages said flange and said arm is lowered from said raised positionand is disengaged from said valve.